1. Field of the Invention
The present invention relates a light emitting device, more particularly to a light emitting device with graded composition hole tunneling layer.
2. Description of the Prior Art
In the prior art structure, most wide band gap semiconductor light emitting devices (particularly Group III and Group V nitride) contain the quantum-well as the light emitting layer. The quantum barrier provides the ability for confining the carrier in the light emitting layer. However, due to the internal electric field will be generated upon operating Group III nitride semiconductor devices, the electrons and holes will be hindered by the declined quantum barrier. The transport of electrons and holes in the quantum-well will be blocked, so that the light emitting efficiency will be reduced.
Employing the quantum-well as the light emitting layer has become a very common application of the semiconductor light emitting device, such as the laser diode and the light emitting diode. It has been mentioned in the prior art that the electron hole distribution of common indium gallium nitride/gallium nitride quantum-well is extremely concentrated in the last quantum-well, which is not advantageous for the operation at high current. It has also been mentioned in the other prior art that the problem of concentrated electrons and holes can be improved by using thin quantum barrier and changing doping concentration, but the efficacy is quite limited. The graded quantum barrier height is adopted to change the carrier transport, but only electron overflow is reduced by this way, the problem of electron hole transport still cannot be improved.